This.
A single session game is a one-off*.
A single-adventure game covering several sessions (e.g. a play-through of a classic module) is just that and no more.
I don't call it a campaign until it gets to multiple adventures and-or multiple parties running within the same setting; adventure paths always qualify as campaigns as despite it all being in the same book (in the WotC publishing model anyway) there's different discrete adventures embedded in there.
* - and usually involves large amounts of beer and some very silly gaming.